In a bowl, pour in the water and milk, reserving a little milk to dissolve the salt. Add the sourdough starter discard in pieces and stir until dissolved.

Place the flour in a mound on a work surface (or in a large bowl), make a well in the center, and add the baking soda (if using). Pour in the water, milk, and starter mixture. Once combined, add the olive oil and mix. Then add the reserved milk with dissolved salt and knead until you have a smooth, even dough.

Transfer the dough to a floured work surface, shape it into a ball, and divide it into 8 pieces, each weighing about 3 1/2 ounces (100 grams). Shape each piece into a ball, cover, and let rest for about 30–40 minutes.

Using a rolling pin, roll each piece into a very thin disk. Brush the surface with extra virgin olive oil, leaving one edge unbrushed. Roll up the disk, starting from the oiled edge, to form a log, making sure the unbrushed edge seals well. Coil each log into a spiral, keeping the seam in the center.

Place the spirals in a covered container and let rest at room temperature for 30–40 minutes. You can store them in the refrigerator in a closed container for a few days and cook them later.

After resting, heat a nonstick skillet or a flat griddle over medium heat. Roll each spiral out as thinly as possible, using flour if needed. Place the flatbread in the hot skillet and cook over low heat for 1–2 minutes per side, flipping once, until lightly golden but still soft. Do not overcook or they will become crispy.

As you cook the flatbreads, stack them on a plate to keep them soft. They are ready to fill and enjoy as you like. You can also make them ahead of time and, once cooled, store them in the refrigerator in a sealed bag. When ready to eat, simply reheat them in a hot skillet on both sides and fill as desired.